A pivot tower irrigation system, also known as center-pivot irrigation, is a method of crop irrigation in which equipment rotates around a pivot while crops are watered by sprinklers. The equipment generally consists of a series of movable towers interconnected by spans with optional corner systems. In many pivot tower irrigations systems, the length of the system is one-quarter mile or longer, and the movable towers are powered by small electric, hydraulic, or water motors. Due to the size of the system, the drivetrain, and the weight of water supported over such a distance, there is significant interest in minimizing the weight of the movable towers and spans themselves. In many pivot tower irrigation systems, the components are made of lightweight steel or aluminum.
Each year invariably brings bouts of severe weather, including high winds. Due to the lightweight construction of the pivot irritation tower system, the high winds may produce sufficient force to topple the movable towers and spans. The resulting impact causes extraordinary damage to the lightweight components, resulting in detrimental financial burdens for farmers and insurance carriers, both in terms of repairing and/or replacing the structure(s), downtime in operations, and/or loss of crop due to lack of water. Therefore, a need exists in the art for an improved pivot irrigation tower system with increased stability under the influence of high winds.
Through analysis of various pivot tower models, it has been determined that the main cause of tipping of pivot tower irrigation systems in strong straight line winds is the excessive drag of the structure high above the ground. This drag is a function of the various components of the structure, with the ground span pipe or tube contributing more than 50% of the drag. The worst case scenario arises when the straight line winds are perpendicular to the span. Also, as the height of the pivot tower system increases, the movement from drag increases. Also, the longer the span, the higher the destabilizing force from strong winds. Conversely, the higher the weight or down force for the structure, the higher wind speed which can be withstood before the structure tips.